In optical devices such as optical microscopes, for example, various functions such as improvement of resolution and aberration correction are realized by using phase modulation of light. Patent reference 1 describes a phase modulation device that modulates phases of light fluxes of a plurality of different wavelengths within a predetermined broad spectrum width. The phase modulation device diffracts the light beam irradiated from the light source via a diffraction grating to different angles for each wavelength. The light beam diffracted for each wavelength enters the spatial phase modulation device through a condenser lens. The phase modulation device has a plurality of phase modulation areas respectively corresponding to the respective wavelengths, and the light flux of each wavelength is enters the phase modulation area corresponding to each wavelength by diffraction via the diffraction grating.